Response of soil microbial diversity to land-use conversion of natural forests to plantations in a subtropical mountainous area of southern China

Land-use conversion can affect the soil microbial community diversity, soil organic matter and nutrient cycling. In this study, soils within a representative land-use sequence were sampled in a subtropical region of China, including four natural forests, Altingia gracilipes Hemsl. (ALG), Cinnamomum chekiangense Nakai (CIC), Castanopsis fargesii Franch. (CAF), and Tsoongiodendron odorum Chun (TSO), and two plantations, Cunninghamia lanceolata (Lamb.) Hook. (CUL) and a citrus orchard (Citrus reticulata Blanco). The soil microbial diversity was investigated by phospholipid fatty acid (PLFA) analysis, denaturing gradient gel electrophoresis (DGGE) and real-time quantitative polymerase chain reaction (PCR). Results showed that microbial community diversity exhibited distinct patterns among land-use types. After conversion of natural forests to plantations, the amount of PLFA and the number of bacterial 16 S rRNA gene copies were reduced significantly, as well as the number of DGGE bands. The average quantity of PLFA was lower by 31% in the CUL plantation and 57% in the citrus orchard, respectively, than in natural forests. Simultaneously, the average copy numbers of the bacterial 16 S rRNA gene were significantly decreased from 8.1 x 10(10) g(-1) dry weight (DW) in natural forest to 4.9 x 10(10) g(-1) DW in CUL plantation, and 3.1 x 10(10) g(-1) DW in the citrus orchard. Such negative responses of soil microbes to conversion of natural forests to plantations could mainly result from decreases in soil organic carbon and necessary elements for growth during land-use conversion, as revealed by statistical analysis. Our results suggested that the soil microbial diversity was indirectly influenced by land-use types in the mid-subtropical mountainous area of southern China. Changes in the amount of litterfall and the soil nutrient status that resulted from land-use conversion drove these indirect changes. Furthermore, deliberate management brought negative effects on soil microbes, which is not beneficial to the sustainability of the ecosystem.